The invention relates to a cast iron alloy for cast iron products with a high thermal stability, the alloy containing, as nonferrous constituents, at least the elements C, Si, Mo, Al and, as admixtures, Ni, Mg and/or S.
In the automotive industry, cast iron alloys are used to produce castings which have to be highly thermally stable, for example the parts which come into contact with the hot exhaust gases from the internal combustion engine. Since internal combustion engines are producing ever higher powers, the exhaust-gas temperatures are becoming ever higher. The exhaust manifolds and casings of turbochargers are exposed to temperatures of 900 to over 1000° C. The transformation temperature, i.e. the temperature at which one type of crystal in the alloy is transformed into another type of crystal, plays an important role at these high temperatures. At the transformation temperature, the volume changes and this volume change leads to irregular expansion characteristics on the part of the castings. The alloys which can be used must have transformation temperatures which are higher than the maximum temperature of use. Austenitic cast steel alloys or alloys with a high nickel content are also used for the abovementioned high use temperatures. Nickel is a relatively expensive raw material. The exhaust manifolds are often also formed from sheet-metal parts, in which case the poor sound insulation makes its presence adversely felt. These solutions are relatively complex to produce.
U.S. Pat. No. 5,236,660 discloses a cast iron alloy of the generic type. The alloy contains approximately 3.1% by weight of C, 4.6% by weight of Si, 1.9% by weight of Al, 1% by weight of Mo and if appropriate also admixtures of Co and Nb.
Working on the basis of this prior art, it is an object of the invention to provide a cast iron alloy which is made from elements which are as inexpensive as possible, the castings having as high a use temperature as possible.